The two species of the genus Dolomedes
are very similar and are only found in or near damp places. Both are
large robust spiders with a strong and imposing appearance. The adults
will take large prey, including bluebottle flies, damselflies, and even
small fishes which the spider attracts to the surface by vibrating the
surface of the water with it's front legs. The males court the females
by waving their front legs alternatively at them for a prolonged display
which culminates in a very brief mating. The female will lay more than
a 1000 eggs in two or more greenish sacs. The spiderlings are pale brown
at first, becoming darker as they grow.

These are the largest spiders found
in Britain with the female gaining a size of 22 mm and the male only
10 - 13 mm. The males are more clearly marked than the females.

These spiders are fairly common in southern
England in areas like swamps or marshes where there is permanent water.
The further north you go the less likely you are to see one of these
beasties.